Organopolysiloxane room temperature vulcanizable (RTV) compositions that are stored under anhydrous conditions will cure upon exposure to water or water vapor at room temperature to yield elastomers. These RTV compositions are prepared by mixing diorganopolysiloxanes having reactive end groups with organosilicon compounds that possess at least three hydrolyzably reactive moieties per molecule. The known RTV compositions are widely used as elastic sealing materials for applications involving the gaps between various joints such as the gaps between the joints of building materials, the joints between structural bodies and building materials in buildings, between the bathtub and wall or floor, cracks on tiles in bathrooms, gaps in the bathroom such as those around the washbasin and those between the washbasin supporting board and the wall, gaps around the kitchen sink and the vicinity, between panels in automobiles, railroad vehicles, airplanes, ships, gaps between prefabricated panels in various electric appliances, machines, and the like. Room temperature vulcanizable silicone sealants thus may be utilized in a wide variety of caulking and sealing applications.
These sealant silicones gradually lose their attractive appearance because of dust and other foreign materials adhering to the surface of the sealant. These adherent materials which consist variously of grime, soaps, detergents, and foods provide nutrients for the growth of surface micro-organisms that further deteriorate the appearance of the sealant, even though the sealant itself is not a nutrient for these micro-organisms. These micro-organisms frequently exhibit colors other than that imparted to the sealant by the use of various pigments, tints and coloring agents, and consequently the sealant suffers a further loss in desirable appearance characteristics.
As a caulking material these sealants are frequently filled with finely divided inorganic materials which may be either reinforcing or non-reinforcing. Reinforcing fillers may be fumed silica, precipitated silica, hydrophobicized precipitated silica, hydrophobicized fumed silica, carbon black, titanium dioxide, ferric oxide, aluminum oxide, and other metal oxides. Non-reinforcing fillers may be calcium carbonate, diatomaceous earth, calcium silicate, zirconium silicate, talc, and bentonite. Fibrous materials such as asbestos, glass fibers, or organic fibers are also useful fillers. The amount of filler used in an RTV composition is selected as desired so as to not interfere with the purposes of the instant invention.
When it is anticipated that these sealant materials will be exposed to conditions that will tend to degrade performance or appearance over a period of time, these sealants are frequently stabilized against such a deterioration by the addition of small quantities of protective additives such as UV stabilizers, anti-oxidants, fungicides, and the like. These additives tend to complement the physical property profile of the sealant by adding additional desirable properties, e.g. resistance to photocatalytic degradation, oxidation (flame retardants), and attack by fungi.
Depending upon the chemical composition of the additive, the application of the sealant containing a particular additive may be restricted to certain types of end uses. For example, sealants containing the fungicide 10, 10'-oxybisphenoxarsine (OBPA) are limited to applications that do not involve food contact. OBPA is highly toxic both by inhalation and by ingestion. It is typically incorporated into the sealant formulation as a dispersion in one of the silicone fluids that are combined to prepare the sealant.
The incorporation of fungicides and mildewstats in sealants is generally necessary because of the moist environments in which these sealants are typically used. The fungicides and mildewcides generally employed in silicone sealants are employed because they possess properties that are toxic to certain micro-organisms that tend to grow in the environment where the sealant is used. Frequently this toxicity extends to the higher vertebrates and thus the application of these sealants is limited to uses where there is little or no risk of danger to human health. Consequently it is desirable to utilize fungicides and mildewstats that are more selective for micro-organisms, i.e. toxic to micro-organisms and not to humans. Such more selective fungicides and mildewstats may be employed in silicone based sealants and utilized in a wider variety of sealant applications because they are less restricted in their fields of use because they should possess little or no toxicity to humans.
While arsenic containing silicone sealants have generally found both widespread and safe application in a variety of kitchen appliances, the consuming public is generally reticent towards their use where food contact or eating utensil contact might conceivably result in contamination. Thus there is a preference on the part of the consuming public for appliances such as dishwashers, refrigerators, freezers and the like that utilize sealants that do not contain toxic elements such as arsenic.
Other more selective fungicidal or anti-microbial materials may render sealant compositions suitable for broader applications. One such more selective compound, di-iodomethyl-para-tolylsulfone has been cleared by the United States Food and Drug Administration (FDA) for use in food contact applications as an ingredient in resinous and polymeric coatings. Thus a sealant containing di-iodomethyl-para-tolylsulfone may be used in conventional sealant applications where an arsenic fungicide containing sealant might be employed or it may be used where contact with food is involved. This broader field of application may result in the use of silicone sealants containing di-iodomethyl-para-tolylsulfone in food processing applications such as commercial kitchens, bakeries and meat processing or packing, particularly since di-iodomethyl-para-tolylsulfone has already been cleared by the U.S. FDA for food contact applications in resins or polymers, viz. sealants.